1. Field of the Invention
The disclosure relates in general to a memory device, a method for manufacturing the same and application of the same, more particularly to a self-rectified device, a method for manufacturing the same, a three-dimensional structure applying with the same and a reading method of a 3D memory device having self-rectified memory cells.
2. Description of the Related Art
A nonvolatile semiconductor memory device is typically designed to securely hold data even when power is lost or removed from the memory device. Various types of nonvolatile memory devices have been proposed in the related art. Also, manufactures have been looking for new developments or techniques combination for stacking multiple planes of memory cells, so as to achieve greater storage capacity. For example, several types of multi-layer stackable thin-film transistor (TFT) NAND-type flash memory structures have been proposed.
Resistive random-access memory (RRAM or ReRAM) is a non-volatile memory type. Resistive memories attract much attention due to its simple MIM (Metal-Insulator-Metal) structure and promising scalability. Different forms of ReRAM have been disclosed, based on different dielectric materials, spanning from perovskites to transition metal oxides to chalcogenides.
Resistive memory device, as the example of the transition metal oxide memory (transition metal oxide resistive memory (TMO ReRAM), and etc.) is a group of two-terminal memory devices that stores the data by different resistance levels. Take a typical ReRAM device with a WSixOy memory and a TiN top electrode for example, hereinafter TiN/WSi3Oy device. FIG. 1 shows a DC bipolar operation of the typical TiN/WSixOy device. The typical TiN/WSixOy device shows very high initial resistance indicating good and uniform oxidation. An initial negative forming voltage is required to bring a high resistance state (HRS) to a low resistance state (LRS). In FIG. 1, the SET state is reached after forming by a negative voltage. Then the cell can be switched in bipolar mode with positive voltage for the RESET state, and negative voltage for the SET state. FIG. 2 shows an AC operation of the typical TiN/WSixOy device. The cell can be switched in bipolar operation like DC switching. The typical TiN/WSixOy device can be reset by applying a positive pulse (to reach the RESET state), and set by applying a negative pulse (to reach the SET state), similar to WOx ReRAM.
FIG. 3 shows the cycling tests with verification of the typical TiN/WSixOy device, and the device being cycled more than 30K times with 10×HRS/LRS ratio. In the cycling tests, the cycling endurance of the typical TiN/WSixOy device is more than 30K times, and 10× resistance window is well maintained by the usual program-verifying algorithm. The TiN/WSixOy ReRAM presents the typical ReRAM property similar to the conventional bipolar ReRAM. When an array with the typical TiN/WSixOy ReRAM is constructed, transistors should be included in the array structure, and each of the transistors functions as the switch of the memory cell.
Additionally, since NAND Flash can stack up vertically with many layers, two-dimensional (2D) ReRAM has little advantage in cost. Three-dimensional (3D) stacking of ReRAM turns out very challenging since (1) the lack of good bipolar selecting device, and (2) the difficulty of decoding a 3D array of 2-terminal devices. Thus, it is also desirable to develop and realize a 2D cross point array and a 3D ReRAM with excellent electrical properties, such as a self-rectifying property, and the reliability and stability of data storage.